Ok, of what i think i understand is that the “s” variable correspond to the “this” and itself correspond to the Array from prototype. It does make sens for me. But the “callback”, it’is the “item” variable ? and foreach “callback( this[x] ) == 1”,
it push it in an new array?

I figured out the exercice because of a previous exemple using callback so i re-adapted it with my own touch (xD) and it worked. But i feel like i playing with dangerous material. It feel uncomfortable, and most importantly in the long run.

note that generally a filter only keeps the values for which the callback returns true or a truthy value. I think adding the == 1 in your if complicates things and won’t make it work like the native .filter, as 1 and truthy values will not be equal in most cases. Simply using